In the related art, an integrated composite filter-cartridge has advantages of a small volume and less joints, which results an increasing application and research of it in a water purification system. However, a post activated carbon filter-cartridge configured for improving a taste in the water purification system is usually positioned outside of the integrated filter-cartridge, which is unbeneficial for miniaturization of a size of a complete machine. In addition, when an insufficient water pressure arises, it is likely to cause a reduced water flux for the whole water purification system, thus a less amount of water yield is resulted and a requirement of the user for a high water flux cannot be satisfied.